Heating elements for high vacuum furnaces



July 26, 1966 c. A. s. HILL HEATING ELEMENTS FOR HIGH VACUUM FURNACESFiled Nov. 7, 1963 INVENTOR. C'II'ARLAFS- A61 H/LL BY @TQW ATTORNEYUnited States Patent 3,263,015 HEATING ELEMENTS FOR HIGH VACUUM FURNACESCharles A. S. Hill, Southampton, Pa., assignor, by mesne assignments, toAbar Corporation, Willow Grove, Pa., a corporation of Pennsylvania(1964) Filed Nov. 7, 1963, Ser. No. 322,205 8 Claims. (Cl. 1325) Thisinvention relates to resistance heating elements for high vacuumfurnaces.

The necessity for heating and melting high temperature refractorymetals, and specifically zirconium, columbium, tantalum, molybdenum,tungsten, titanium, rhenium, and alloys thereof, which require heatingin a vacuum not only for degassing the metal but to prevent undesiredreaction, requires the use of vacuum furnaces.

'Serious temperature limitations have been imposed by actual operatingconditions on most of the heating elements heretofore available.

In my prior application Serial No. 202,616, filed June 14, 1962, nowPatent No. 3,155,758, there is shown animproved heating element withwhich higher furnace operating temperatures are made available thanheretofore. The heating element there shown has limitations,particularly in that it is not as well suited as is desired forelectrode materials which are difiicult to weld.

The heating element of the present invention has added advantages overthose heretofore available.

It is the principal object of the present invention to provide aresistance heating element for vacuum furnaces which is of simpleconstruction and which will permit attaining higher temperatures thanheretofore, which will have a longer useful life and which will be freefrom other difiiculties heretofore encountered in this field.

It is a further object of the present invention to provide a resistanceheating element for vacuum furnaces, which accommodates the elevatedtemperatures with negligible distortion, which has an improved uniformcurrent input distribution for energization, and which has otherimproved qualities in use.

It is a further object of the present invention to provide aresistanceheating element for vacuum furnaces which is simple in construction,sturdy, and free from difiiculties in use. I i It is a further object ofthe present invention to provide a resistance heating element for vacuumfurnaces which permits the use, in an effective manner, of materialswhich are difiicult to weld.

It is a further object of the present invention to provide an improvedheating element for vacuum furnaces which is freely suspended so as topermit rapid replacement or interchange of heating elements.

It is'a further object of the present invention to provide resistanceheating elements for vacuum furnaces which can be readily interchangedso as to substitute one kind of resistance material for another therebyincreasing the versatility of the furnace.

It is a further object of the present invention to provide an improvedheating element for vacuum furnaces which permits of the use of a widerange of thickness of heating element, including very thin elements,with reduction of power cost and cost of furnace components.

It is a further objectof the present invention to provide an improvedmounting for heating elements of vacuum furnaces which is exceedinglysimple and avoids the necessity for welding or fusion joining of marginsof the element.

It is a further object of the present invention to provide an improvedheating element for vacuum furnaces in which the length of the elementcan be selected to match the power supply with elements of differentresistivity.

It is a further object of the present invention to provide a resistanceheating element for vacuum furnaces which is supported in a manner whichdecreases the likelihood of failure.

It is a further object of the present invention to provide a resistanceheating element for vacuum furnaces which is supported in a pendantrelation in an improved manner.

It is a further object of the present invention to provide a resistanceheating element for vacuum furnaces which can be used in furnaces fortension testing at high temperatures and for other purposes.

Other objects and advantageous features of the invention will beapparent from the description and claims.

The nature and characteristic features of the invention will be morereadily understood from the following description taken in connectionwith the accompanying drawings forming part thereof, in which:

FIGURE 1 is a view in perspective of a portion of a vacuum furnacehaving the heating element of the invention mounted therein;

FIG. 2 is a horizontal sectional mately on the line 2-2 of FIG. 1;

FIG. 3 is a fragmentary perspective view of the heating elementpartially assembled;

FIG. 4 is an enlarged fragmentary sectional view taken approximately onthe line 44 of FIG. 3; and FIG. 5 is a fragmentary perspective view of amodified form a free suspended heating element in accordance with theinvention.

It should, of course, be understood that the description and drawingsherein are illustrative-merely and that various modifications andchanges can be made in the structure disclosed without departing fromthe spirit of the invention.

Like numerals refer to like parts throughout the several views.

Referring now more particularly to FIGS. 1 to 4 of view taken approxithedrawings, the furnace and its vacuum equipment have,

been omitted and only the heating element and its associated structureare illustrated. As there shown, an outer water cooled heat sink isprovided which comprises opposite pairs of vertical metallic side walls10, 11, 12 and 13, preferably in connected contiguous pairs for outwardswinging so that access can be had to the interior. The walls 10, 11, 12and 13 can be supported in any desired outer furnace enclosure (notshown) and preferably have liquid cooling pipes 14 mounted thereon withcooling liquid supply and delivery pipes 15 and 16.

Within the interior of the pairs of walls 10, 11, 12 and 13, spacedmetallic shields 17 can be provided having notches 18 at their uppermargins aligned with corresponding notches 19 in the side walls 10, 11,12 and 13 Electrodes 20, 21, 22 and 23 are provided, are supported inany desired manner, are preferably liquid cooled, and have sockets 24for the reception of hori zont-al heating elementmounting rods 25. Themounting rods 25 are of L-shape with holding arm portions 26 and innerelement supporting arm portions 27. The holding arm portions 26 of therods 25 can be clamped attheir outer ends in the electrodes 20, 21, 22and 23, respectively, and held in any desired manner, such as by setscrews 28. The holding arm portions 26 extend inwardly through thenotches 19 and 18, and the arm portions 27, preferably disposed in thesame horizontal plane with the portions 26 and with each other, have theheating elements 30 freely pendant therefrom.

The rods 25 can be of any desired electric conductive material capableof functioning at the elevated temperatures in the furnace, and can beof the same metal as the heating elements 30 or of different metals.

The heating elements 30 can be of nickel, molybdenum, columbium,tantalum, tungsten, tantalum-tungsten alloys such as 90% tantalum andtungsten, tungsten-rhenium alloys, rhenium, osmium, iridium, or alloysincluding binary or ternary alloys of these metals, it is also intendedfor some purposes to employ conductive nonmetals, so long as these havethe desired temperature resistant qualities in use and the desiredresistivity.

The heating elements 30 are preferably of material in sheet form, and ofthe desired thickness in accordance with the heating qualities desired.For example, sheet metal of thickness down to about one half athousandth of an inch may be employed.

The use of relatively thin sheet material permits of using less powerfor heating as well as lesser qualities of high cost per pound materialfor the heating elements.

The heating elements 30 are supported by the arm portions 27 and inpendant relation thereto and at their upper ends, as shown in detail inFIG. 4, can have elongated cylindrical sections 31 with seams 32therealong, such as are employed on sheet metal containers, to retainthe cylindrical sections 31 at elevated temperatures.

The heating elements 30, at the bottoms thereof, can have similarcylindrical sections 33 for the reception of L-shaped horizontallydisposed connector rods 34 of any suitable material, and preferably thesame as that employed for the rods 25.

In the form of the invention shown in FIG. 5, the heating elements 30::are shown as sleeves, pendant from the rod portions 27, and with theconnector rods 34 supported thereby as before.

In use, the electrodes 20 and 21 can be connected in one phase of thesource of electric energy and the electrodes 22 and 23 can be connectedto the same phase or to another phase.

The electric energy supplied through the pairs of electrodes 20, 21, 22,and 23, and through the rods 25, and by the connection through the rods34 is effective for resistance heating of the heating elements 30 or 30athe heating action being available in the space enclosed by the elements30 or 30a.

As the heating of the heating elements 30 or 30a occurs, with expansiondue to temperature increase, the heating elements 30 or 30a arerelatively free from restraint, horizontally considered, and likewiseare free from vertical restraint.

The manner of suspension of the heating elements 30 and 30a on the rods25 and with the lower connector rods 34 loosely mounted therein permitsof quick interchange of heating elements so that a heating element ofone composition can be substituted for that of another composition, orcross section, with the substituted element, if of differentresistivity, of a length to match the power supply, if desired.

Operating temperatures up to 3000 C. can be accomplished by selection ofsuitable length of the heating element. The direct heat transfer fromthe heating elements 30 and 30a to the rods 25 is reduced because of thesmall cross sectional area of the rods 25 for heat transfer.

The construction of heating elements heretofore de scribed have auniformity of current distribution with improved resistance heatingaction. Further, by reason of the uniformity of heating, they have asubstantially uniform temperature profile. Freedom from distortion bothupon heating and cooling is accordingly attained.

I claim:

1. A resistance heating device for vacuum furnaces comprisingelectrodes,

a matched pair of upper horizontal supporting rods respectivelyconnected to said electrodes,

a matched pair of resistance heating elements in sheet form extendingdownwardly from said upper supporting rods,

a common lower horizontal connecting rod engaging the lower ends of saidpair of elements,

said elements each having a curved upper end portion and a curved lowerend portion extending re spectively around the upper and lower rods.

2. A resistance heating device as defined in claim 1 in which saidheating elements are freely slidable along said upper rods for insertionand removal thereof.

3. A resistance heating device as defined in claim 2 in which said lowerconnecting rod is freely slidable along the lower ends of said elements.

4. A resistance heating device as defined in claim 1 in which saidcurved end portion is a cylindrical sleeve.

5. A resistance heating device as defined in claim 1 in which theheating elements are each sleeve shaped.

6. A resistance heating device as defined in claim 1 in which said upperand lower end portions are cylindrical, and

said heating elements each has a central section of a single thicknessof material with seams at the top and bottom thereof connecting saidcentral section with said upper and lower end portions.

7. A resistance heating device for vacuum furnaces comprising aplurality of electrodes,

a plurality of matched pairs of upper horizontal supporting rodsrespectively connected to said electrodes,

matched pairs of resistance heating elements for each of said pairs ofsupporting rods,

said heating elements being in sheet form and extending downwardly fromsaid upper supporting rods,

said heating elements each having a curved upper and a curved lower endportion and said upper end portions being in slidable engagement withsaid supporting rod,

a common lower horizontal connecting rod of L-shape for each matchedpair of heating elements engaging the lower ends of said pair ofelements,

said connecting rods being in slidable engagement with said lower ends.

8. A resistance heating device as defined in claim 7 in which saidheating elements each has a central section of a single thickness ofmaterial with seams at the top and bottom thereof connecting saidcentral section with said upper and lower end portions.

References Cited by the Examiner UNITED STATES PATENTS 1,401,303 12/1921Baldwin 219-538 1,819,554 8/1931 Hanson 3-25 2,264,716 12/1941 Roth 3-25X 2,749,424 6/ 1956 Dieterich 325 X 2,966,537 12/1960 Witucki et al. 325X 3,057,936 10/1962 Hill 3-25 3,155,758 11/1964 Hill 325 3,178,6654/1965 Matheson et al 3-25 RICHARD M. WOOD, Primary Examiner. ANTHONYBARTIS, Examiner.

V. Y. MAYEWSKY, Assistant Examiner.

1. A RESISTANCE HEATING DEVICE FOR VACUUM FURNACES COMPRISINGELECTRODES, A MATCHED PAIR OF UPPER HORIZONTAL SUPPORTING RODSRESPECTIVELY CONNECTED TO SAID ELECTRODES, A MATCHED PAIR OF RESISTANCEHEATING ELEMENTS IN SHEET FORM EXTENDING DOWNWARDLY FROM SAID UPPERSUPPORT RODS, A COMMON LOWER HORIZONTAL CONNECTING ROD ENGAGING THELOWER ENDS OF SAID PAIR OF ELEMENTS,